Power amplifier



Nov. 9 1926. 1,606,212

F. w. DUNMORE El AL POWER AMPLIFIER Filed March 21, 1922 J/mmalo IA/710W.

0M 13.3mm

for vwq 26 to provide means Pasti -9, 9%

I {STATES PATENT I, 11,606,212 a OFFICEQV "runners w. rumour: museum; 1 nownnn, or wasnmerou, msrmcrr or i conuurm.

rowan. mrnrr na. l

' Application autumn e1, 19st. swarm. 545L493;

' Our invention relates to apparatus. for the amplification and reproduction of ,soundsby electrical means and more articularly to an amplifying ,unit and 'repro ucer of electrical signals, p The ob'ect of our invention is to an a'mpli er and reproducer in the a readily portableiunit.

Another ob'ect of our invention is to pro- Provide orm of t'ide an amplifier of the thermionic vacuum tube type with circuit arran ements for op erating theapparatus fromt 1e usual source of alternating-currentresidence power su ply for energizing the vacuum tube circuits l5 wlthout the use of primary or secondary batteries.

A.further object of the invention is to provide a circuit arrangement for a thermionic vacuum tube amplifier employing a 20 10nd speaking reproducer in which theloud speaker has its field winding energized from a source of residence lightin power without the use of primaryor secondary batteries. I A stillfurther object of the invention is p I for eliminating the hum of e low frequency alternating current power supply in the circuits of ,the thermionicvacuum tube amplifier and reproucern' I 8 Anothercb ject of the invention'is to pro-- yide means for rectifying alternating currentand smoothing out -.t erectified energy to provider. source of power for the circuits. of -=th'e 'spealizing reproducer.

-The invention will p be more clearly under stood by reference to the following specification andaccompanying drawings, in which Figure '1 is a wiring diagram of the amlifier. and electricalreproducer 'arran ed or connection to a source of alternating current power supply with means for .eliminating the hum of the 'alternatin current power supply, and Fig. 2 is a mo ification showing a wiring diagram of the apparatus illustratin means in the thermionic vacuum tube circuits for eliminating the hum ofthe' V alternatin current powersu'ppl a -j i It wille understoodfthat the-principles of our invention may be embodied in 'various forms and that details are not mate rial. The present embodiment of vention, therefore, isto be considered as 7 merely indicative.

the drawing and hereinafter'described in dc thermionic vacuum tubes and loud The form illustrated in tail has been found to be one of the ractlcal embodiments and capable of e cie'nt' operation and practical in construction. lhe apparatus of the present invention comprises a readily portable unit having terminals for the connection of the equipment to any source of electrical variations required to be amplified and electrically re- .produced at increased amplitude through a 0nd speaki-n telephone. ,The unit includes .a plurality o thermionic vacuum tubes con-' 'nected incircuit for audio frequency amplification. -The land speaking telephone may be of the type employing a coilarmature and electroma etic field coil. A pair of terminals is provided for theconnection of the unit we source of alternating current poiversuppl as, for example, the usual 110 volt 60 cyc e supply. The power is con-j ncted to the primary winding of a trans-, former having proportionate windings thereon for energizing the various circuits of the unit. The filaments of tlie amplifier tubes are energized from one of these windlugs. Rectifiers are employed in the unit whereby enerjgr derived from other-windin'gs is rectifie and supplied as a source of platecircuit potential for the vacuum tube amplifier and as a su ply for energizing the field of the loud spea g reproducer,' The rectifiers are preferabl of the two electrode .valve construction and have their filaments we energized from other windin on the transformer. Means are provide for biasing the grids oi the vacuumtubes" comprising'the,.e0 amplifier. Means are also included in the cireuits'oi the amplifier for eliminating the; hum from the a ternating current power supply and means are included in the equip-;- ment for smoothin out the rectified energy Referringto the circuit diagram shown in "Figure 1, reference characters 1 and 2 indicate the input terminals of the audio frel quency amplifier, and lead .-to the primary winding of the audio frequency transformer 14a. The secondary terminals of'transformer "4 ers connected to the gridof-vacuum tube .5 and to the'slider of the stabilizing -rheo"- stat 11 through batte 12' respectively. The battery 12 connecte in series with the slider of rheostat lllztas a potential oi about ioi volts so connected that a negative'volt q "age is impressed on'the grid of tube .5. The I lo purpose of stabilizer 11 is to keep the normal voltage of the grid at a steady value with respect to the filament and eliminate the hum of the alternating current supply while the negative voltage from battery 12 holds the grid at its best potential for am,- plifying purposes. As this battery furnishes grid voltage only, the power drawn from it is negligible. It is therefore of the small flash light battery type and will continue efiective fora period equivalent to its normal shelf life. The primary winding of audio frequency transformer 6 is connected in the output or plate circuit of vacuum tube 5. The secondary of audio frequenc transformer 6 is connected to the grid tube 7 and to stabilizer 11, with series grid battery 12, functioning the same as in the first stage.

- winding 24 to which the speaking In the output or the primary of the is connected, of winding. This transformer also serves to reduce the hum of the alternating current supply. The secondary of this transformer ma be connected to an type of loud speaking reproducer. In t e resent instance a loud speaker having a fiel windin may be employed and this secondary winding may lead to the primary winding of a stepdown transformer employed wit the loud speaker, the secondary winding of which leads to the armature coil 9 as is usual in this instrument.

'29 is -a transformer having a primary 110 volt, 60 cycle A. C. ower is applied at terminals 27 and 28. inding 22 supplies the filament voltage 'for the rectifier tube 18, rheostat 19 being in series to. regulate its brilliancy. Winding 21 supplies high voltage for the lates of the amplifier tubes 5 and 7., said igh voltage being rectified by. tube 18 and smoothed out by condenser 16 which is about 4 microfarads ca acity, and achoke coil 17. This provides a igh voltage direct current which is suitable for'the plates of the amplifying tubes.

Winding plate circuit of tube 7 telephone transformer 8 20 provides the for lightin the filaments o the amplifier tubes 5 an 7, and their brilliancy is controlled by rheostat 15.

Reference numeral 10 represents the electro-magnetic field coil of the loud speaker and is excited by low voltagedirect current supplied by the tungar rectifier tube 14.

The filament of this tube is lighted from.

winding 25 of transformer 29 and winding 26 supplies the proper voltage which is rectified by tungar tube 14 and applied to the field winding 10. I

In spite of the fact that the sole source of power for this circuit is from the 60 cycle alternating current source, there is practically no resultant hum in the loud telephone due to the reactance ofwhich has a one to one ratio roper voltage trans ormer fered by the winding 10 and the cooperative effect of this winding with the output circuit of the amplifier system. That is to say the inductance of the field coil 10 is selected of such value and the ower amplifier is so connected with the winding 9 that pulsations in the field winding are effectively opposite in phase to the phase of the pulsations in the output circuit of the amplifier so that there is a tendency for the disturbing currents to be neutralized as a result of which the armature remains stationary so far as the effects of disturbing current components are concerned.

' A modified form of this circuit is shown in Fig. 2, wherein there is a condenser 36 of about .02 microfarads capacity shunted by a leak resistance of about 2 megohms, in

.grid at a suitable value for amplifying audio frequency energy impressed at terminals 1 and 2,-at the same time acting as a partial block to any existing low frequency hum. The leak resistance prevents the grid from becoming supercharged.

L In the plate circuit of tube 5, in series with the primary of the audio frequency transformer 6, is a condenser 32 of about .02 microfarads shunted by a resistance of approximately 80,000 ohms. This condenser serves to partially block the 60 cycle hum, but allows the higher frequencies to pass through. .The shunt resistance allows the direct currentplate voltage to reach the platearound the condenser, but serves as a block to the low frequency hum.

In series with the secondary of the audio frequenc transformer 6 in the grid circuit of tube a is a .02 ,microfarad condenser 31 shunted by a 2 nie'gohm resistance. This condenser and leak 31 function the same as condenser and leak 36in eliminating any low frequency hum.

A .02 microfarad condenser shunted by an 80,000 ohm resistance 34: is in series with the plate circuit of tube 7 and functions in the same manner as condenser and resistance 32 toeliminate any residual low frequency hum.

Condenser 35 is about .005 microfarads capacity and is in series with the secondary of the telephone transformer 8. It also serves as a partial 'block to any low frequenc hum which may be present. The 29 is arranged with terminals 27 and 28 for connection to the usual source of 110 volt A. C. residence lighting power and includes the several proportionate windings for supplying energy to the circuits of 'the unit as described in Fig. 1.

iao

lee

cuit of a detector tube in a radio receiver.

11 and 30 are adjusted to an electrical midoint the point in the resistance, at which tubes 5 voltage impressed on the grido and 7 from the A. C. supply is steady or of very small value. By this adjustment the bum is eliminated from the reproducer'circuits. The audio frequency energy variations supplied to terminals 1 and 2 are reproduced at great volume of sound by the reproducer comprising windings 9 and 10. J

It will be understood th it we are not limited to the use of a reproducer employing a field winding but that any type of reproducer may be employed The disturbing pulsations which may be present in the winding 9 are of opposite phase by virtue of the phase shifting circuit 89, than the phase of disturbing pulsations or currents in the winding 10. The mutual effect therefore is nil as the pulsations tend to be men'- tralized and have no efl'ect upon the arma ture.

The entire equipment, including the reproducing horn of the loud speakenk is adapted for mounting within a readily portable cabinet.

-Having thus described our invention what we claim and desire to secure, by Letters Patent of the United States is-as follows:

1. In an apparatus for the reproduction of sound, the combination of a thermionic vacuum tube amplifier circuit, a power source of alternating current, means for rectifyingsaid current, means for supplying the rectified current to said vacuum tube amplifier circuit, a loud speakerreproduced of the elect-rod namic ty e connected to said amplifier, and means or supplying rectified current to said reproducer.

2. In an apparatus for the reproductionof sound, a thermionic vacuum tube amplifier, an input circuit. an output circuit, a power source of alternating current, means for rectifying said current, a loud speaker reproducer connected in said out ut circuit and comprising an armature win ing and a field winding and circuits for supplying said rectified current to said output circuit and to said field winding, said windings being connected in such relation that disturbing current effects in said loud speaker reproducer are substantially eliminated.

3. In an apparatus for the reproduction of sound, a thermionic vacuum tube amplifier, an input circuit and an output circuit, aloud speaker reproducer comprising an armature winding and a field winding,

connections between said output circuit and said armature winding, :1 power source of alternating current, means for rectifying said current and supplying said rectified current to said output circuit and to said field winding, said windings being so conneoted with said means as to substantially oppose the effect of disturbing currents in said loud speaker reproducer.

4. In an apparatus for the reproduction of sound, a thermionic vacuum tube amplifier, an input circuit, an output circuit, a power source of alternating current, a plurality of means for rectifying said current, filters for smoothing out the rectified current and supplying said rectified current to said out of: circuit, means in said output circuit or reproducing the signal energy and connections whereby one of said rectifiers supplies ener y to said re roducing means, said repro' ucing means eing arranged to substantially neutralize disturbing currents.

5. In an apparatus for the reproduction of sound, a thermionic vacuum tube amplifier, an input circuit, and output circuit, a loud speaker reproducer comprising an armature winding and a field winding, connections between said output circuit and said armature winding, a power source of alternating current, means for rectifying said current, means for smoothing out the rectified current and sup lying said current to said output circuit an said field winding with the alternating current components thereof in phase opposition whereby the effect of said'alternating current components on said loud speaker reproducer are substantially eliminated.

6. In an a paratus for the reproductio of sound, a t ermionic vacuum tube amplifier, an input circuit, an output circuit, a ower source of alternating current, means or rectifying said current filters for reducing the hum of the rectified current, and supplying said rectified current to said output circuit, a loud speaker in said output circuit for reproducing the signal energy and means connected to said loud speaker and associated with said power source for opposing the residual hum of the rectified current.

7. A sound reproducing apparatus comprising in combination an electron tube am: phfication system including a filament heat ing circuit, an output circuit, a loud speaker sound reproducer having a pair of windings, one of said windings connected with said output circuit, and connected to a source of alternating current, a device for rectifying a portion of said current for supplying the rectified currentto the other of said aforementioned windings, means for deriving power from said source for energizing said filament heating circuit and said output circuit, said first mentioned winding being connected with said output circuit in such manner that interfering current pulsations occur therein in substantially opposite phase with respect to interfering current pulsations in said second winding for neutralizing the effects of said interfering current pulsations upon said sound reproducing apparatus.

8. An electromagnetic sound reproducing system comprising in combination a power amplifier having circuits arranged to be excited from a power source of alternating current, a loud speaker reproducer including a circuit energized from said power source and a circuit connected with said power amplifier, said last mentioned circuit including a condenser and a transformer having primary and secondary windings with the primary winding connected with said power amplifier and said secondary winding connected with said reproducer and arranged in combination of an amplifier, a

such manner that alternating current components existent in said circuits occur in substantially opposite phase whereby the efiects of said alternating current components on said loud speaker reproducer are substantially neutralized.

9. In a sound reproducing apparatus the loud speaker having armature and field winding with said armaturewinding connected to the output of said amplifier, an alterating current supply source, means for deriving power from said source for energizing the circuits of said amplifier, filter circuits for reducing the hum of said alternating current in said apparatus and means for su plying power from said source to said fie d winding in such manner that the residual hum in said field winding will oppose the residual hum in said armature winding for eliminating the hum of said alternating'current in said apparatus.

FRANCIS \V. DUNMORE. PERCIVAL D. LOVELL.

power from said source for energizing said filament heating circuit and said output circuit, said first mentioned winding being connected with said output circuit in such manner that interfering current pulsations occur therein in substantially opposite phase with respect to interfering current pulsations in said second winding l'or neutralizing the effects of said interfering current pulsations upon said sound reproducing apparatus.

8. An electromagnetic sound reproducing system comprising in combination a power amplifier having circuits arranged to be excited from a power source of alternating current, a loud speaker reproducer including a circuit energized from said power source and a circuit connected with said power amplitier, said last mentioned circuit including a condenser and a transformer having primary and secondary windings with the primary winding connected with said power amplifier and said secondary winding connected with said reproducer and arranged in such manner that alternating current components existent in said circuits occur in substantially opposite phase whereby the effects of said alternating current components on said loud speaker reproducer are substantially neutralized.

9. In a sound reproducing apparatus the combination of an amplifier, a loud speaker having armature and field winding with said armaturewinding connected to the output of said amplifier, an altcrating current supply source, means for deriving power from said source for energizing the circuits of said amplifier, filter circuits for reducing the hum of said alternating current in said apparatus and means for sup plying power from said source to said field winding in such manner that the residual hum in said field winding will oppose the residual hum in said armature winding for eliminating the hum of said allernating'current in said apparatus.

FRANCIS \V. DUNMORIC. PERCIVAL D. LOWE LL.

Certificate of Correction.

It is hereb certified that in Letters Patent No. 1,606,212, granted November 9,

1926, upon t e application of Francis W. Dunmore and Percival D. Lowell, of

Washington, District of Columbia,

for an improvement in Power Amplifiers,

errors appear in the printed specification requiring correction as follows: Page 3, l1ne 46, clalm 1, for the word reproduced read reproducer, and line 93, claim 5, for the word and read an; and that the said Letters Patent should be read with these corrections therein that. the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 14th day of December, A. D. 1926.

[sun] M. J. MOORE, Aatmg Comissiomr of Patents.

DISCLAIMER 1,606,212.Fra ncis l V. Dunmore and Percival D. Lowell, Washington, I). C lownn AMPLIFIER. Patent dated November 9, 1926. Disclaimer filed August 16. 1938, by the patentees and the exclusive licensee, Dubilier (ondenser (Tarporation Hereby enter this disclaimer to any "electrodynamic type of loud speaker as set forth in claim 1 except such as includes a field winding and a coacting armature winding and wherein the field winding offers substantial reactance to the effects of alternating current hum. a

To any field winding as set forth in claims 2, 3, 5, and 9, except such as offers a substantial reactance to the effects of alternating current hum.

To any reproducing means" as set forth in claim 4, except such as includes :1 field winding and an armature winding and wherein the field winding oflers substantial reactance to the effects of alternating current hum.

To any loud speaker as set forth in claim 6, except such as includes a field winding and a coacting armature winding and wherein the field winding offers substantial reactance to; the e'fi'ects of alternating current hum.

To any loud s I aker sound reproducer having a pair of windings as set forth in claim 7, except su%as employs one of the windings as a reactance for substantially reducing the effects o galternating current hum.

To any loudspeaker reproducer as set forth in claim 8, except such as includes a winding offering a substantial reactance to the effects of alternating current hum.

[Oflicial Gazette September 6, 1.938.] 

